Bake a Tape?
You might ask what baking a tape is all about. First off, good question. To explain baking, we must first uncover abit of dark history in the recording industry. Magnetic tape used in recording media, be it video or audio, analogue ordigital, is made of three basic componants. There’s the base which is usually polyester which is an artificialplastic but sometimes it can also be cellulose triacetate which is the sameorganic plastic used in photographic film or even paper. There is also some kind of magnetic materialsuch as ferricoxide (normal rust), chromium dioxide, fersoferric oxide(magnetite) and many others. Thismagnetic material has to be held onto the base with some kind of binder orglue. There is also usually some kindof lubricant on the tape to help things move along but more on that later. In the late 70’s, it was determined that usingpolyurethane would yield better sonic results than the traditional binder beingused until that time.
Polyurethanebinder was in theory a good idea. However, there are many different types of complex urethane moleculechains. Longer chains produce a verythick, heavy gum that is essentially useless for making recording media. Short urethane chains were too thin and hada tendancy to absorb moisture from the air. Medium chains seem to be the best. The problem is that back then, the only way to figure out the length ofthe urethane molecule chains was to measure the viscocity, that is, how runnythe binder was. Therefore, an evenmixture of long chains with short chains will appear to be pure mediumchains. Now, until the mid 80’s whenthe “high pressure gas chromatograph” was invented, they were finally able todetermine the true content of the urethane binders being used. Therefore, there was about a decade’s worthof tape that developed what they called “hydrolysis”, AKA "sticky shedsyndrome". Most tapes during thisperiod can live about ten years but some went south in a matter of a few daysif the binder had purely short urethane chains mixed with long chains and nomedium chains.
One can determine what “sticky shed syndrome” means. What actually happens is the short binderchains which had obsorbed the moisture separates from the rest of the tape andcomes to the surface of the magnetic coating. Even though this newly formed film is only a few molecules thick, thetape gets sticky and it sheds the magnetic material quite easily. Tapes with this condition create quite a mess and there is nocure. Minor hydrolysis will cause thetape transport to be somewhat sluggish and the tape guides and heads will getdirty very quickly. Severe cases willbring the transport to what is literally a screaming hault. The tape can shed the magnetic coating soseverely that the audio or video disappears into a wad of brown oblivion. In most cases, transport is diffucult andclarity is moderately reduced. Again,there is no cure for tapes with this problem but there is a temporary fix thatwill allow some one enough time to remix or remaster to a new medium. This fix is called baking.
Baking is in a sentence, raising the temperature of themedium to a level where the water can evaporate out of the tapecomposition. Now, since the shortmolecule chains are still at the surface of the tape, hydrolysis returns veryquickly. However, the tape will atleast be usable for a short time. Theprocess of baking tape is a very precise and delicate procedure. The tape must be heated to the point wherethe moisture can evaporate but without damaging the tape. If the tape is overheated, it can warp, thelubricants can break down and in the worse case cenario, the magnetic field ofthe tape itself can deteriorate or print through to other parts of the tape. There is a very narrow margine in which properbaking can occur. Therefore it isimperitive to follow the procedure exactly, otherwise a very valuable piece ofhistory or even a sentimental recording could be lost forever.
The temperature must be maintained between 130 and 140degrees Fahrenheit. Any lower and theprocess will do nothing. Higher thanthat, and print through (among other things) becomes emanant. It is also very important to ensure that thetape is packed as close to properly as possible to prevent warping (that is,played to the end, tail out). This isnot always possible as playing an effected tape will cause further damage. Therefore, a compromise must be made. The temperature must be maintained preciselyto ensure the tape will survive the treatment. Conventional ovens can spike 50 degrees or more in a matter of a fewseconds so they cannot be used. Thetape must be heated in an environment that is relatively free from alternatingelectromagnetic fields. Using alightbulb in an insulated box will not be acceptable either as the requiredproximity to the tape puts the magnetic medium in direct line of fire with thepulsating magnetic radiation of the coiled tungsten filaments. Large convection ovens are a much betteralternative but even they are not always reliable enough and the thermometersare still lacking. The temerature mustbe monitored carefully to prevent spiking. Normal cylindrical food dehydrators are a step in the right directionbut they need a bit of modification to work properly.
The time involved in baking tape is much lesscritical. It still makes a differenceand the time varies by the size of the tape itself of course. A ¼” tape will take between one and fourhours to bake depending on how bad it is. ½” tape should be baked two to five hours. 1” tape will need between three and six hours while 2” shouldget four to eight hours. The generalrule of thumb is to start with the ¼” time standards and add ½ an hour forevery ¼” you add to the width. It isrecommended to lean toward longer times as shorter times may not besufficient. Baking for periods longerthan the specified increments have negligible negative effect. Tapes should be flipped about every hour ofbaking until the time has expired. Allow several hours for the tape to return to normal room temperaturebefore restoring them to operation. Youmay notice some minor crackling sounds when the tape is played. This is usually a minor issue with theurethane at the surface causing the tape to stick slighly to the adjacentsurface. It can be hazardous, howeverwhen winding at high speed so it is recommended to simply play the tape all theway through once before attempting higher shuttle speeds.
While baking tape is a realatively simple process thatmost people can do, it should be left to a professional if the user isuncertain of the process or their respective equipment. Please note that any time GCM recieves atape that requires baking, it will be done for a small fee after gainingapproval from the client. GCMfrequently bakes older tapes and has always been able to successfully transferthem after the fact. However, noguarantees will be made over the condition of the tape or the success of thetransfer thereafter.
1/4": 1-4 hours
1/2": 2-5 hours
1" : 3-6 hours
2" : 4-8 hours
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